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8aa853d5c1
freebsd/share/man/man4/sa.4
Kenneth D. Merry 43518607b2 Significant upgrades to sa(4) and mt(1). 
The primary focus of these changes is to modernize FreeBSD's
tape infrastructure so that we can take advantage of some of the
features of modern tape drives and allow support for LTFS.

Significant changes and new features include:

 o sa(4) driver status and parameter information is now exported via an
   XML structure.  This will allow for changes and improvements later
   on that will not break userland applications.  The old MTIOCGET
   status ioctl remains, so applications using the existing interface
   will not break.

 o 'mt status' now reports drive-reported tape position information
   as well as the previously available calculated tape position
   information.  These numbers will be different at times, because
   the drive-reported block numbers are relative to BOP (Beginning
   of Partition), but the block numbers calculated previously via
   sa(4) (and still provided) are relative to the last filemark.
   Both numbers are now provided.  'mt status' now also shows the
   drive INQUIRY information, serial number and any position flags
   (BOP, EOT, etc.) provided with the tape position information.
   'mt status -v' adds information on the maximum possible I/O size,
   and the underlying values used to calculate it.

 o The extra sa(4) /dev entries (/dev/saN.[0-3]) have been removed.

   The extra devices were originally added as place holders for
   density-specific device nodes.  Some OSes (NetBSD, NetApp's OnTap
   and Solaris) have had device nodes that, when you write to them,
   will automatically select a given density for particular tape drives.

   This is a convenient way of switching densities, but it was never
   implemented in FreeBSD.  Only the device nodes were there, and that
   sometimes confused users.

   For modern tape devices, the density is generally not selectable
   (e.g. with LTO) or defaults to the highest availble density when
   the tape is rewritten from BOT (e.g. TS11X0).  So, for most users,
   density selection won't be necessary.  If they do need to select
   the density, it is easy enough to use 'mt density' to change it.

 o Protection information is now supported.  This is either a
   Reed-Solomon CRC or CRC32 that is included at the end of each block
   read and written.  On write, the tape drive verifies the CRC, and
   on read, the tape drive provides a CRC for the userland application
   to verify.

 o New, extensible tape driver parameter get/set interface.

 o Density reporting information.  For drives that support it,
   'mt getdensity' will show detailed information on what formats the
   tape drive supports, and what formats the tape drive supports.

 o Some mt(1) functionality moved into a new mt(3) library so that
   external applications can reuse the code.

 o The new mt(3) library includes helper routines to aid in parsing
   the XML output of the sa(4) driver, and build a tree of driver
   metadata.

 o Support for the MTLOAD (load a tape in the drive) and MTWEOFI
   (write filemark immediate) ioctls needed by IBM's LTFS
   implementation.

 o Improve device departure behavior for the sa(4) driver.  The previous
   implementation led to hangs when the device was open.

 o This has been tested on the following types of drives:
	IBM TS1150
	IBM TS1140
	IBM LTO-6
	IBM LTO-5
	HP LTO-2
	Seagate DDS-4
	Quantum DLT-4000
	Exabyte 8505
	Sony DDS-2

contrib/groff/tmac/doc-syms,
share/mk/bsd.libnames.mk,
lib/Makefile,
	Add libmt.

lib/libmt/Makefile,
lib/libmt/mt.3,
lib/libmt/mtlib.c,
lib/libmt/mtlib.h,
	New mt(3) library that contains functions moved from mt(1) and
	new functions needed to interact with the updated sa(4) driver.

	This includes XML parser helper functions that application writers
	can use when writing code to query tape parameters.

rescue/rescue/Makefile:
	Add -lmt to CRUNCH_LIBS.

src/share/man/man4/mtio.4
	Clarify this man page a bit, and since it contains what is
	essentially the mtio.h header file, add new ioctls and structure
	definitions from mtio.h.

src/share/man/man4/sa.4
	Update BUGS and maintainer section.

sys/cam/scsi/scsi_all.c,
sys/cam/scsi/scsi_all.h:
	Add SCSI SECURITY PROTOCOL IN/OUT CDB definitions and CDB building
	functions.

sys/cam/scsi/scsi_sa.c
sys/cam/scsi/scsi_sa.h
	Many tape driver changes, largely outlined above.

	Increase the sa(4) driver read/write timeout from 4 to 32
	minutes.  This is based on the recommended values for IBM LTO
	5/6 drives.  This may also avoid timeouts for other tape
	hardware that can take a long time to do retries and error
	recovery.  Longer term, a better way to handle this is to ask
	the drive for recommended timeout values using the REPORT
	SUPPORTED OPCODES command.  Modern IBM and Oracle tape drives
	at least support that command, and it would allow for more
	accurate timeout values.

	Add XML status generation.  This is done with a series of
	macros to eliminate as much duplicate code as possible.  The
	new XML-based status values are reported through the new
	MTIOCEXTGET ioctl.

	Add XML driver parameter reporting, using the new MTIOCPARAMGET
	ioctl.

	Add a new driver parameter setting interface, using the new
	MTIOCPARAMSET and MTIOCSETLIST ioctls.

	Add a new MTIOCRBLIM ioctl to get block limits information.

	Add CCB/CDB building routines scsi_locate_16, scsi_locate_10,
	and scsi_read_position_10().

	scsi_locate_10 implements the LOCATE command, as does the
	existing scsi_set_position() command.  It just supports
	additional arguments and features.  If/when we figure out a
	good way to provide backward compatibility for older
	applications using the old function API, we can just revamp
	scsi_set_position().  The same goes for
	scsi_read_position_10() and the existing scsi_read_position()
	function.

	Revamp sasetpos() to take the new mtlocate structure as an
	argument.  It now will use either scsi_locate_10() or
	scsi_locate_16(), depending upon the arguments the user
	supplies.  As before, once we change position we don't have a
	clear idea of what the current logical position of the tape
	drive is.

	For tape drives that support long form position data, we
	read the current position and store that for later reporting
	after changing the position.  This should help applications
	like Bacula speed tape access under FreeBSD once they are
	modified to support the new ioctls.

	Add a new quirk, SA_QUIRK_NO_LONG_POS, that is set for all
	drives that report SCSI-2 or older, as well as drives that
	report an Illegal Request type error for READ POSITION with
	the long format.  So we should automatically detect drives
	that don't support the long form and stop asking for it after
	an initial try.

	Add a partition number to the sa(4) softc.

	Improve device departure handling. The previous implementation
	led to hangs when the device was open.

	If an application had the sa(4) driver open, and attempted to
	close it after it went away, the cam_periph_release() call in
	saclose() would cause the periph to get destroyed because that
	was the last reference to it.  Because destroy_dev() was
	called from the sa(4) driver's cleanup routine (sacleanup()),
	and would block waiting for the close to happen, a deadlock
	would result.

	So instead of calling destroy_dev() from the cleanup routine,
	call destroy_dev_sched_cb() from saoninvalidate() and wait for
	the callback.

	Acquire a reference for devfs in saregister(), and release it
	in the new sadevgonecb() routine when all devfs devices for
	the particular sa(4) driver instance are gone.

	Add a new function, sasetupdev(), to centralize setting
	per-instance devfs device parameters instead of repeating the
	code in saregister().

	Add an open count to the softc, so we know how many
	peripheral driver references are a result of open
       	sessions.

	Add the D_TRACKCLOSE flag to the cdevsw flags so
	that we get a 1:1 mapping of open to close calls
	instead of a N:1 mapping.

	This should be a no-op for everything except the
	control device, since we don't allow more than one
	open on non-control devices.

	However, since we do allow multiple opens on the
	control device, the combination of the open count
	and the D_TRACKCLOSE flag should result in an
	accurate peripheral driver reference count, and an
	accurate open count.

	The accurate open count allows us to release all
	peripheral driver references that are the result
	of open contexts once we get the callback from devfs.

sys/sys/mtio.h:
	Add a number of new mt(4) ioctls and the requisite data
	structures.  None of the existing interfaces been removed
	or changed.

	This includes definitions for the following new ioctls:

	MTIOCRBLIM      /* get block limits */
	MTIOCEXTLOCATE	/* seek to position */
	MTIOCEXTGET     /* get tape status */
	MTIOCPARAMGET	/* get tape params */
	MTIOCPARAMSET	/* set tape params */
	MTIOCSETLIST	/* set N params */

usr.bin/mt/Makefile:
	mt(1) now depends on libmt, libsbuf and libbsdxml.

usr.bin/mt/mt.1:
	Document new mt(1) features and subcommands.

usr.bin/mt/mt.c:
	Implement support for mt(1) subcommands that need to
	use getopt(3) for their arguments.

	Implement a new 'mt status' command to replace the old
	'mt status' command.  The old status command has been
	renamed 'ostatus'.

	The new status function uses the MTIOCEXTGET ioctl, and
	therefore parses the XML data to determine drive status.
	The -x argument to 'mt status' allows the user to dump out
	the raw XML reported by the kernel.

	The new status display is mostly the same as the old status
	display, except that it doesn't print the redundant density
	mode information, and it does print the current partition
	number and position flags.

	Add a new command, 'mt locate', that will supersede the
	old 'mt setspos' and 'mt sethpos' commands.  'mt locate'
	implements all of the functionality of the MTIOCEXTLOCATE
	ioctl, and allows the user to change the logical position
	of the tape drive in a number of ways.  (Partition,
	block number, file number, set mark number, end of data.)
	The immediate bit and the explicit address bits are
	implemented, but not documented in the man page.

	Add a new 'mt weofi' command to use the new MTWEOFI ioctl.
	This allows the user to ask the drive to write a filemark
	without waiting around for the operation to complete.

	Add a new 'mt getdensity' command that gets the XML-based
	tape drive density report from the sa(4) driver and displays
	it.  This uses the SCSI REPORT DENSITY SUPPORT command
	to get comprehensive information from the tape drive about
	what formats it is able to read and write.

	Add a new 'mt protect' command that allows getting and setting
	tape drive protection information.  The protection information
	is a CRC tacked on to the end of every read/write from and to
	the tape drive.

Sponsored by:	Spectra Logic
MFC after:	1 month
2015-02-23 21:59:30 +00:00

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.\" Copyright (c) 1996
.\" Julian Elischer <julian@FreeBSD.org>. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd February 12, 2015
.Dt SA 4
.Os
.Sh NAME
.Nm sa
.Nd SCSI Sequential Access device driver
.Sh SYNOPSIS
.Cd device sa
.Sh DESCRIPTION
The
.Nm
driver provides support for all
.Tn SCSI
devices of the sequential access class that are attached to the system
through a supported
.Tn SCSI
Host Adapter.
The sequential access class includes tape and other linear access devices.
.Pp
A
.Tn SCSI
Host
adapter must also be separately configured into the system
before a
.Tn SCSI
sequential access device can be configured.
.Sh MOUNT SESSIONS
The
.Nm
driver is based around the concept of a
.Dq Em mount session ,
which is defined as the period between the time that a tape is
mounted, and the time when it is unmounted.
Any parameters set during
a mount session remain in effect for the remainder of the session or
until replaced.
The tape can be unmounted, bringing the session to a
close in several ways.
These include:
.Bl -enum
.It
Closing a `rewind device',
referred to as sub-mode 00 below.
An example is
.Pa /dev/sa0 .
.It
Using the MTOFFL
.Xr ioctl 2
command, reachable through the
.Sq Cm offline
command of
.Xr mt 1 .
.El
.Pp
It should be noted that tape devices are exclusive open devices, except in
the case where a control mode device is opened.
In the latter case, exclusive
access is only sought when needed (e.g., to set parameters).
.Sh SUB-MODES
Bits 0 and 1 of the minor number are interpreted as
.Sq sub-modes .
The sub-modes differ in the action taken when the device is closed:
.Bl -tag -width XXXX
.It 00
A close will rewind the device; if the tape has been
written, then a file mark will be written before the rewind is requested.
The device is unmounted.
.It 01
A close will leave the tape mounted.
If the tape was written to, a file mark will be written.
No other head positioning takes place.
Any further reads or writes will occur directly after the
last read, or the written file mark.
.It 10
A close will rewind the device.
If the tape has been
written, then a file mark will be written before the rewind is requested.
On completion of the rewind an unload command will be issued.
The device is unmounted.
.El
.Sh BLOCKING MODES
.Tn SCSI
tapes may run in either
.Sq Em variable
or
.Sq Em fixed
block-size modes.
Most
.Tn QIC Ns -type
devices run in fixed block-size mode, where most nine-track tapes and
many new cartridge formats allow variable block-size.
The difference between the two is as follows:
.Bl -inset
.It Variable block-size:
Each write made to the device results in a single logical record
written to the tape.
One can never read or write
.Em part
of a record from tape (though you may request a larger block and read
a smaller record); nor can one read multiple blocks.
Data from a single write is therefore read by a single read.
The block size used
may be any value supported by the device, the
.Tn SCSI
adapter and the system (usually between 1 byte and 64 Kbytes,
sometimes more).
.Pp
When reading a variable record/block from the tape, the head is
logically considered to be immediately after the last item read,
and before the next item after that.
If the next item is a file mark,
but it was never read, then the next
process to read will immediately hit the file mark and receive an end-of-file notification.
.It Fixed block-size:
Data written by the user is passed to the tape as a succession of
fixed size blocks.
It may be contiguous in memory, but it is
considered to be a series of independent blocks.
One may never write
an amount of data that is not an exact multiple of the blocksize.
One may read and write the same data as a different set of records.
In other words, blocks that were written together may be read separately,
and vice-versa.
.Pp
If one requests more blocks than remain in the file, the drive will
encounter the file mark.
As there is some data to return (unless
there were no records before the file mark), the read will succeed,
returning that data.
The next read will return immediately with a value
of 0.
(As above, if the file mark is never read, it remains for the next
process to read if in no-rewind mode.)
.El
.Sh BLOCK SIZES
By default, the driver will NOT accept reads or writes to a tape device that
are larger than may be written to or read from the mounted tape using a single
write or read request.
Because of this, the application author may have confidence that his wishes
are respected in terms of the block size written to tape.
For example, if the user tries to write a 256KB block to the tape, but the
controller can handle no more than 128KB, the write will fail.
The previous
.Fx
behavior, prior to
.Fx
10.0,
was to break up large reads or writes into smaller blocks when going to the
tape.
The problem with that behavior, though, is that it hides the actual on-tape
block size from the application writer, at least in variable block mode.
.Pp
If the user would like his large reads and writes broken up into separate
pieces, he may set the following loader tunables.
Note that these tunables WILL GO AWAY in
.Fx 11.0 .
They are provided for transition purposes only.
.Bl -tag -width 12
.It kern.cam.sa.allow_io_split
.Pp
This variable, when set to 1, will configure all
.Nm
devices to split large buffers into smaller pieces when needed.
.It kern.cam.sa.%d.allow_io_split
.Pp
This variable, when set to 1, will configure the given
.Nm
unit to split large buffers into multiple pieces.
This will override the global setting, if it exists.
.El
.Pp
There are several
.Xr sysctl 8
variables available to view block handling parameters:
.Bl -tag -width 12
.It kern.cam.sa.%d.allow_io_split
.Pp
This variable allows the user to see, but not modify, the current I/O split
setting.
The user is not permitted to modify this setting so that there is no chance
of behavior changing for the application while a tape is mounted.
.It kern.cam.sa.%d.maxio
.Pp
This variable shows the maximum I/O size in bytes that is allowed by the
combination of kernel tuning parameters (MAXPHYS, DFLTPHYS) and the
capabilities of the controller that is attached to the tape drive.
Applications may look at this value for a guide on how large an I/O may be
permitted, but should keep in mind that the actual maximum may be
restricted further by the tape drive via the
.Tn SCSI
READ BLOCK LIMITS command.
.It kern.cam.sa.%d.cpi_maxio
.Pp
This variable shows the maximum I/O size supported by the controller, in
bytes, that is reported via the CAM Path Inquiry CCB (XPT_PATH_INQ).
If this is 0, that means that the controller has not reported a maximum I/O
size.
.El
.Sh FILE MARK HANDLING
The handling of file marks on write is automatic.
If the user has
written to the tape, and has not done a read since the last write,
then a file mark will be written to the tape when the device is
closed.
If a rewind is requested after a write, then the driver
assumes that the last file on the tape has been written, and ensures
that there are two file marks written to the tape.
The exception to
this is that there seems to be a standard (which we follow, but do not
understand why) that certain types of tape do not actually write two
file marks to tape, but when read, report a `phantom' file mark when the
last file is read.
These devices include the QIC family of devices.
(It might be that this set of devices is the same set as that of fixed
block devices.
This has not been determined yet, and they are treated
as separate behaviors by the driver at this time.)
.Sh IOCTLS
The
.Nm
driver supports all of the ioctls of
.Xr mtio 4 .
.Sh FILES
.Bl -tag -width /dev/[n][e]sa[0-9] -compact
.It Pa /dev/[n][e]sa[0-9]
general form:
.It Pa /dev/sa0
Rewind on close
.It Pa /dev/nsa0
No rewind on close
.It Pa /dev/esa0
Eject on close (if capable)
.It Pa /dev/sa0.ctl
Control mode device (to examine state while another program is
accessing the device, e.g.).
.El
.Sh DIAGNOSTICS
None.
.Sh SEE ALSO
.Xr mt 1 ,
.Xr cam 4
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written for the
.Tn CAM
.Tn SCSI
subsystem by
.An Justin T. Gibbs
and
.An Kenneth Merry .
Many ideas were gleaned from the
.Nm st
device driver written and ported from
.Tn Mach
2.5
by
.An Julian Elischer .
.Pp
The owner of record for many years was
.An Matthew Jacob .
The current maintainer is
.An Kenneth Merry
.Sh BUGS
This driver lacks many of the hacks required to deal with older devices.
Many older
.Tn SCSI-1
devices may not work properly with this driver yet.
.Pp
Additionally, certain
tapes (QIC tapes mostly) that were written under
.Fx
2.X
are not automatically read correctly with this driver: you may need to
explicitly set variable block mode or set to the blocksize that works best
for your device in order to read tapes written under
.Fx
2.X.
.Pp
Partitions are only supported for status information and location.
It would be nice to add support for creating and editing tape partitions.
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